Known tractors comprise an internal combustion engine for generating torque in order to rotate a driving axle and possibly drive one or more external devices attached to a power take-off of the tractor. A transmission system is provided for transmitting power from the engine to the driving axle and/or to the power take-off. The transmission system may comprise a continuously variable transmission (CVT), particularly of a hydrostatic type.
A crankshaft of the engine is connected to a shaft of the transmission system by a damping assembly. The damping assembly comprises a damper that is used to deflect and absorb engine vibrations, in order that torque may be transmitted to the transmission system more smoothly.
Angular speed of the crankshaft varies according to a periodic waveform. Angular speed of the transmission shaft downstream of the damping assembly also varies according to a periodic waveform. However, due to the damping assembly, a phase difference exists between angular speed of the crankshaft and angular speed of the transmission shaft.
The damping assembly may comprise a detector for detecting torque which is transmitted from the engine to the transmission system. The detector measures the phase angle at the damping assembly, i.e. the phase difference between angular speed of the crankshaft and angular speed of the transmission shaft.
Once the phase angle has been measured, torque at the damping assembly can be determined by means of a characteristic curve which, for a given damper, gives the relationship between phase angle and torque.
The detector of the damping assembly needs to be calibrated, in order to measure the real value of the phase angle and hence obtain the real value of the torque, in any working condition. The value of torque so obtained can be subsequently used for a number of different purposes.
A calibration method is known in which the phase angle is measured at two different working points, with the clutch completely or almost completely engaged and the brakes activated. The two working points at which the phase angle is measured correspond to different values of torque generated by the engine. High torque values are selected for the two working points, such as, for example, 300 N·m and up to 1000 N·m respectively. The transmission system is therefore subjected to considerable stress.
Furthermore, since the known calibration method is carried out while the clutch is engaged, wear on the clutch components is produced.
Finally, the known calibration method is not particularly accurate, both because only two working points are taken into consideration and because of the manner in which data relating to the two working points are processed.
An object of the invention is to improve known vehicles, particularly working vehicles such as wheeled or crawler tractors and excavators.
Another object is to provide a method for calibrating a detector included in a damping assembly of a vehicle, in which the components of the vehicle and particularly the transmission system thereof are subjected to reduced stress.
A further object is to provide a method for calibrating a detector included in a damping assembly of a vehicle, which involves substantially no wear on the clutch.
Another object is to provide a method for calibrating a detector included in a damping assembly of a vehicle, which produces accurate and reliable results.